Production of lactic acid from lignocellulosic biomass using bacterial isolates

Abstract

Present research work was aimed at utilization of lignocellulosic biomass i.e. rice straw, wheat straw and eucalyptus leaf litter for production of value added product i.e. lactic acid. Rice straw, wheat straw and eucalyptus leaf litter were collected from and nearby villages of Thapar University, Patiala. Using xylose as substrate for lactic acid production from environmentally isolated bacterial strains, maximum lactic acid yield obtained is 0.432g/l using DGN2 bacterial isolate by utilizing 50g/l xylose. Biomass pre-treatment plays a important role in a lignocellulosic feed-stock based biorefinery for processing of cellulose, hemicelluloses and lignin into chemicals and biofuels. Acid and alkali hydrolysis of rice straw, wheat straw and eucalyptus leaf litter biomass was done to get hydrolysates. Reduction in residual concentration of sugar after inoculation with NA9 was observed maximally in dilute acid hydrolysate of wheat straw as reducing sugar content decreased from 1.090 mg/ml to 0.180 mg/ml. the increasing trend in content of protein after inoculation with NA9 was reported maximally in concentrated acid hydrolysate of eucalyptus leaf litter as protein content increased from 0.340 mg/ml to 0.680 mg/ml. Cost effective production of optically pure lactic acid from lignocellulosic sugars is commercially attractive. Environmentally isolated bacterial strains were used to produce lactic acid by utilising sugars from hydrolysate of rice straw, wheat straw and eucalyptus leaf litter obtained after pre-treatment with acid and alkali at 50ºC without agitation after inoculation with NA9 and DGN2 bacterial isolates. The maximum yield of lactic acid was reported from concentrated acid hydrolysate of eucalyptus leaf litter after inoculation with NA9 i.e. 5.5 g/l. This is concluded that NA9 (Bacillus licheniformis) is promising strain for lactic acid production and eucalyptus leaf litter biomass is promising substrate for lactic acid production.